Smallest even k such that lpf(k-3) > lpf(k-1) >= prime(n), where lpf=least prime factor (A020639).

Terms

a(0) =10a(1) =26a(2) =50a(3) =170a(4) =170a(5) =362a(6) =362a(7) =842a(8) =842a(9) =1370a(10) =1370a(11) =1850a(12) =1850a(13) =2210a(14) =3722a(15) =3722a(16) =3722a(17) =4892a(18) =5042a(19) =7082a(20) =7922a(21) =7922a(22) =7922a(23) =10610a(24) =10610a(25) =10610a(26) =11450a(27) =13844a(28) =16130a(29) =16130